The need for an economically attractive and environmentally acceptable process for treating wastes, particularly chromium ore wastes, has grown more pressing. Indeed, states have strict environmental regulations; see, for instance, Code of Maryland Regulations, 10.51.02.17F, and appendices thereto and Samplers and Sampling Procedures for Hazardous Waste Streams, EPA 600/02-80-018 (January 1980).
Serious environmental problems are currently being experienced because of the waste products resulting from the processing of chromium ore. Chrome ore is generally processed on an industrial scale by high temperature alkaline roasting under oxidizing conditions. The sodium chromate formed thereby is leached from the roast and converted to bichromate via acid treatment, and thence to chromic acid via a separate acid treatment. In proceeding through the roasting and acid treatment steps, there is generated a final leached waste residue containing residual toxic hexavalent chromium values which present a significant disposal problem.
Various processes for treating these waste materials have focused on complex and costly procedures.
Such known processes include forming a mixture of the waste material, a silicate, and a cementitious agent in the presence of water and allowing the mixture to harden into an aggregate of stoney concretion wherein the pollutant waste is said to be encapsulated. Although the thus obtained aggregates satisfy certain standards required for environmental protection, such aggregates suffer from major drawbacks in that rupture or fragmentation, resulting from transportation or actual use, will release the encapsulated toxic waste from the stoney concretion. The thus released toxic substances may once again present an environmental hazard particularly if the waste material contaminates ground water, streams, rivers, lakes and the like. A further drawback of such processes resides in the fact that after a period of time the concretions exhibit or undergo disintegration, thereby again releasing toxic materials to the surrounding environment.
Other processes focus on achieving a chemical reaction between metallic ions and substantially monosilicic or disilicic acid which is said to thereafter polymerize the waste material into a disposable form. An example of such a process is described in U.S. Pat. No. 4,404,105 (1983). One of the drawbacks to this process is that the reaction is apparently slow, is competitive with alternative reaction mechanisms, and requires specific adequate physical chemical conditions in order to avoid gel formation.
A still further process for pretreating hazardous waste comprises placing unopened waste containers in a vessel containing a liquid pretreatment media therein and subjecting the so situated containers to an agitation process which ruptures the unopened containers so as to deposit the contents thereof into the vessel for reaction with the liquid pretreatment media. Such a process is described in U.S. Pat. No. 4,284,514 (1981).
Another procedure, described in U.S. Pat. No. 4,377,483 (1983), comprises using slag from steel manufacture to remove heavy metals contained in waste water such that the metals are absorbed on the slag. The slag is then formed into solid blocks, ballast or aggregate by admixture with Portland cement or alumina cement.
An alternative process, described in U.S. Pat. No. 3,803,032 (1974), comprises treating harmful water soluble chromates contained in water-leached residue from the roasted product obtained by alkali oxidizing roasting of chrome ore to insolubilize and fix said chromate in said residue by mixing lumpy and/or powdery water-leached residue with organic materials capable of being converted into active carbon, roasting the thus formed mixture in a gaseous atmosphere having low oxygen concentration at a gas temperature of from 400.degree. to 1000.degree. C. and a material temperature of 400.degree. C. to 700.degree. C. and thereafter quenching the thus roasted product.
Other efforts to effect treatment of waste solutions are described in U.S. Pat. No. 3,755,530 (1973) which teaches removing solids from waste solutions of metal finishing processes by freezing globules or droplets from the solutions and removing the solvent from the frozen globules or droplets via sublimation.
However, none of these prior art processes provides a disposal method as efficient or as economically attractive as the present invention especially when consideration is given to the fact that the present invention not only significantly or essentially completely reduces the toxicity of the hexavalent chromium values of a waste material component but also provides, ultimately, a product which has good load supportive properties when combined with mud or sludge dredged from salty or brackish water or even fresh or swamp water and finely ground basic granulated blast furnace slag.
Heretofore, in the dredging of harbors or other bodies of water for the purpose of deepening the channels to improve navigation or for the installation of large pipes or tunnels, large quantities of accumulated slimy sludges or bay muds must be removed. These sludges or muds contain very finely divided suspended solid particles. Such solids, because of their finely divided physical state, are not usable as a landfill material in that they have poor load supportive properties. Consequently, a distressing sludge disposal problem is presented.
The present invention thus provides a solution to both the chromium ore waste treatment problem and the sludge and mud disposal problem.